That green is a layer of blue-green algae. Most years around August sections of Lake of the Woods get covered over by the stuff, sometimes inches thick.

Anthony runs Ballard's Resort where the Rainy River flows into Lake of the Woods. It's a fishing outpost on the edge of Minnesota's northern border a short boat ride away from Canada.

“It could be in my head, but we always seem to think it's getting thicker and thicker.”

Nick Anthony

After 15 years on the water, he said there's a perception among some locals that algae blooms are getting worse.

"It could be in my head, but we always seem to think it's getting thicker and thicker," he said as waited at Ballard's polished wooden bar recently for an afternoon bus-load of out-of-state businessmen.

Recent research findings suggest the algae growth might not be in Anthony's head. Scientists don't yet know exactly how much blooms have expanded, but early findings suggest the algae is getting thicker, likely due to a combination of climate change and decades-old pollution.

Tracking the progress of algae growth

The algae bloom findings came from the Lake of the Woods Water Sustainability Foundation's state of the basin report, which integrates five years of private and government research. The behemoth document, released earlier this month, covers all kinds of lake issues. According to Todd Sellers, executive director of the foundation, algae blooms are a chief worry.

Canadian researchers mapping algae growth patterns using satellite imagery have yet to show any conclusive proof of bloom expansion, so until recently, there wasn't much cause for concern. Satellite imagery, while a fantastic tool for tracking changes in a 1,679 square mile lake, is pretty new.

But the satellite pictures only go back to 2006, Sellers said. In just eight years, long-term trends might not show up.

New research, he said, takes a longer view. Researchers drove long pipes into the lake bed, extracting core samples and examining layers of sediment for pigments and the tiny glass-like exoskeletons left behind by deceased algae.

"Sediments are laid down annually on the lake bottom," he said, "just like rings on a tree."

Sellers said those cores read like a lake timeline showing greater and greater algae growth over the last few decades. Exact growth figures will require more study, but already, he said researchers have some idea of what might be causing the likely increases.

“Certainly, Lake of the Woods is a dramatic demonstration of climate change.”

Todd Sellers

Algae growth patterns mirror steady warming trends in the lake, according to the report. Since the 1960's, the lake has lost a month of freeze over. That's an extra month every year for water to heat up, and for algae to soak up the sun.

"Certainly, Lake of the Woods is a dramatic demonstration of climate change," he said.

The green slime, he said, requires warm water, plenty of sunlight and finally, a good amount of phosphorous. Warming temperatures, Sellers said, provided the first two sides of what he described as an algae trifecta. Decades of pollution provided the last element.

Phosphorous, a nutrient vital to algae growth is also a by-product of the logging industry. In most circumstances, Sellers said regulations could diminish algae blooms by limiting the amount of phosphorous flowing into the lake. That won't work in Lake of the Woods.

Damage already done

Environmental regulations begun in the 1960s cut phosphorous in the Rainy River, the lake's largest tributary. The river's been clean for half a century, but the damage is already done. There's apparently enough phosphorous in the lake already to support blooms.

Kit BeckelJohn Enger/MPR News

At this point there's not a whole lot that can be done. Sellers worries if the lake continues to warm, the blooms could continue to worsen. The stuff isn't great to look at and has what Anthony described only as a "very specific smell." But the problem could mean more than some bad smells.

Heavy blooms block other lake plants from the sun, and if they get large enough could kill off deep-water fish. Rotting algae, Sellers said, sucks oxygen from lake depths. If enough algae dies and settles at once, the fishery will start to suffocate.

Seller's worries though, aren't shared by those who make their living on the lake. Anthony doesn't think the algae has hurt fishing, or that it might in larger volumes. Some others don't even think the blooms are getting worse.

"We've always had algae," said Kit Beckel.

Beckel started guiding fishing trips at his father's resort when he was 11 years old, 54 years ago. He said that place, called Trail's End, burned down long ago. Now he guides for Sportsman's Lodge, just down the road from Ballard's.

Early one morning last week he readied one of the lodge's hefty fiberglass launches. He loaded one cooler of bait, and another cooler of sandwiches for the group of Floridian tourists waiting on shore.

He said a lot about the lake has changed in half a century. Fish got bigger when commercial fishing was quashed in the 1980s, and bigger still with DNR slot limits. Fishing hot spots shifted, but the algae, he said that hasn't changed at all.

Back in the 70s he said there were years the bloom was so thick, his boat didn't even make a wake. Even Sellers said centuries old journals kept by explorers and fur traders describe southern sections of the lake covered over with something akin to grass clippings.

"It's always been a very productive lake," Sellers said. He's just worried the algae might be getting too productive.